1. Field of the Invention
The present invention relates to an ultrasonically bonded fabric and a method of making the same.
2. Description of the Related Art
Converting fabrics by ultrasonic bonding using a horn and anvil roller is known. This is taught, for example, in U.S. Pat. No. 4,406,720 and 4,414,045 to Wang et al. Ultrasonic bonding has been used in bonding waist bands on disposable diapers. As a reciprocating horn approaches its timed mating with a rotating anvil, the fabric to be bonded is pinched. As the fabric moves across the face of the horn, excess energy often develops therebetween. This excess energy causes problems with "burn through" or otherwise weakening of the bond.
To a certain extent, this burn through problem can be solved by balancing the amount of contact between the horn and the fabric with the amount of energy expended in the bonding process. Also, increasing the basis weight of the fabric can aid in alleviating the burn through problem.
In addition to the burn through problem, tearing problems are prevalent in ultrasonically bonded fabrics. However, the tearing does not tend to occur within the actual bond site, but rather beyond the outer edge of the site.
The tearing is attributed to the development of mechanical stress in the fabric. When the horn and anvil come together the fabric at the bond site is held tight, while the fabric downstream of the bond site is being drawn away. As such, excessive stress is placed on that part of the fabric immediately adjacent the bonding mechanism on the downstream side which may cause the fabric to tear.
It has been observed that carded fabrics that contain crimped fibers overcome this tearing problem by allowing a small, sudden extension of the crimped fiber to alleviate the stress on the fabric at the instant it is pinched by the bonding mechanism.
However, with spunbonded non-woven fabric this stress cannot be relieved by the extension of a crimp. The stress must be borne solely by the fabric. Indeed, it is at this point (i.e., where the fabric undergoes ultrasonic bonding), that the fabric is weakest and susceptible to tearing. Convertability of a fabric by ultrasonic bonding is the ability to produce bonded fabrics without fabric failure, i.e., burn through or tearing.
It is therefore an object of the present invention to overcome the disadvantage of the prior art and to provide an improved ultrasonically bonded fabric and method of making the same.
It is another object of the invention to improve the convertibility of non-woven fabrics in an ultrasonic bonding process.
It is a further object of the present invention to reduce the stress developed in a non-woven fabric during ultrasonic bonding.
It is a still further object of the present invention to enhance the lubricity of a non-woven fabric.
It is another object of the present invention to improve the liquid transport properties of the non-woven component of the bonded fabric.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.